The present invention relates to a position control system in a D.C. motor.
In order to precisely control the position in a D.C. motor, the D.C. motor is generally controlled in two modes. The first mode is the speed detection mode wherein the rotating speed of the motor is controlled so that the motor rotates to a desired position at a fast speed. The second mode is the position detection mode, which is conducted after the completion of the speed detection mode. In the position detection mode, the motor position is precisely controlled so that the motor stops at the desired position.
In the conventional system, the speed detection mode and the position detection mode are controlled in the analog fashion. Therefore, the conventional system is not suited for the LSI technique. Furthermore, in the conventional system, the motor speed control in the speed detection mode is conducted by the frequency control method. The frequency control method inevitably produces the steady-state deviation between the instructed rotating speed and the actual rotating speed of the D.C. motor. The steady-state deviation varies depending on the load connected to the D.C. motors. Thus, the conventional system can not ensure a stable oeration when the load connected to the D.C. motor varies.
Accordingly, an object of the present invention is to digitalize a control circuit for a position control system in a D.C. motor.
Another object of the present invention is to provide a D.C. motor position control system which precisely controls the position of the D.C. motor and stops the D.C. motor at a desired position.
Still another object of the present invention is to provide a D.C. motor position control system which ensures a stable operation even when the load connected to the D.C. motor varies.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a rotary encoder is associated with a D.C. motor so as to develop an approximate sinusoidal position indicating, analog signal in response to the rotation of the D.C. motor. The approximate sinusoidal position indicating, analog signal is introduced into a slice level determination circuit which develops two sliced position indicating, digital signals to a main control circuit. The following system is digitally controlled with reference to the sliced position indicating, digital signals.
In a preferred form, a phase-locked-loop (PLL) control is employed in the speed detection mode. The phase-locked-loop (PLL) control does not produce the steady-state deviation between the actual rotating speed of the D.C. motor and the instructed speed. Therefore, an accurate speed control is achieved even when the load connected to the D.C. motor varies.